1. Field of the Invention
The present invention relates to an imaging environment recognition device that provides a vehicle onboard system using an onboard camera, such as an obstacle detection system or a parking support system, with necessary environmental information by using an imaging means, such as a camera, for imaging road conditions surrounding the vehicle and processing the image taken to recognize imaging environment.
2. Description of the Related Art
Research and development activities have been underway for recent years to provide automatic driving of vehicles and vehicle driving aid. Techniques have being studied for notifying drivers of the presence of a pedestrian by processing images taken by an onboard camera for detecting pedestrians. Techniques are also being studied for providing driving aid by detecting obstacles, traffic lights, and traffic signs.
When images are taken by such an onboard camera, fog may occur, or a lens of the onboard camera mounted on an outside of the vehicle or a window disposed forward of the onboard camera mounted on an interior of the vehicle may be covered with water droplets from rain. The fog or water droplets can make the images taken by the onboard camera less sharp, thus hampering proper detection of obstacles and traffic signs. It therefore becomes important to warn the driver of the imaging environment by recognizing water droplets and the like present within a field of view of the camera because of rainfall and to improve quality of the images by removing the water droplets and the like.
Conventionally known is a technique that detects contamination of a window glass or rainfall to achieve the foregoing purposes, as disclosed in JP-A-11-326541. According to the known art, a traffic lane is detected in order to detect contamination of a window glass forward of an onboard camera or rainfall. A degree of defocus of the traffic lane is thereby obtained. The degree of defocus obtained is then compared with that when the visibility is good. Contamination of the window glass or rainfall is thereby determined. In addition to the technique detecting contamination of the window glass forward of the camera and the like, a technique is known for detecting water droplets deposited on the lens of a camera mounted on the outside of the vehicle. Such a technique is disclosed in JP-A-2000-355260. The technique calculates an optical flow of an image taken by the onboard camera and determines that an object containing therein water is deposited if a velocity vector suddenly appears in a region close to the camera in the calculated optical flow.